(a) Field of the Invention
The present invention relates to a laminate type photosensitive material for use in electrophotography.
(b) Description of the Prior Art
As the photosensitive material for use in electrophotography, there have hitherto been known the so-called dispersion-type photosensitive material prepared by coating a dispersion obtained by dispersing a relatively large quantity of inorganic photoconductive substance such as zinc oxide, titanium oxide, cadmium sulfide, etc. in an appropriate binder on a conductive support, the so-called evaporative-type photosensitive material prepared by depositing an inorganic photoconductive substance such as selenium, selenium alloy, etc. through vacuum evaporation on a conductive support, and the organic photosensitive material prepared by coating an organic photoconductive substance such as poly-N-vinyl carbazole or derivatives thereof, and derivatives of polyphenylene pyrazole, polyvinyl anthracene, polyvinyl pyrene, oxazole, oxadiazole, pyrazole or imidazole, anthracene, tetraphene, pyrene, etc. on a conductive support.
However, the dispersion-type photosensitive material is defective in that it is inferior in surface smoothness and mechanical strength due to its large content of inorganic photoconductive substance. The evaporation-type photosensitive material is defective in that the cost of manufacturing thereof is high and the stability of the photoconductive substance used therein is questionable. And, as to the organic photosensitive material, although it is admittedly superior to the foregoing dispersion-type photosensitive material and evaporative-type photosensitive material in flexibility, light transmissibility, etc., it is defective in that the practical electrophotographic sensitivity thereof is generally poor and therefore it is still unsuitable for extensive use.
With a view to improving the foregoing defects of the conventional photosensitive materials, a variety of the so-called laminate-type photosensitive materials for use in electrophotography have recently been proposed. These laminate-type photosensitive materials can be classified broadly into 3 types. Photosensitive materials of the first type include ones prepared by interposing a barrier layer consisting essentially of metal oxide, polyamide, polyurethane, acrylic resin, polystyrene or the like in between a support and a photoconductive layer in order to control the dark decay and ones prepared by forming an adhesive layer consisting essentially of polyamide, polyester, vinyl acetate resin, cellulose type resin, polyvinyl alcohol or the like in order to improve the adhesion between a support and a photoconductive layer or forming a protective layer consisting of a resin such as cellulose-type resin, polyvinyl acetal, silicone resin, polyester, vinyl chloride resin, vinyl acetate resin, polystyrene, acrylic resin, polyamide or the like on the photoconductive layer (the latter ones are also useful in the modified processes of NP, PIP, polarity reversing process, etc. other than Carlson's type process). Photosensitive materials of the second type include ones prepared by forming a resin layer as an electrically insulating layer which consists essentially of polyethylene terephthalate, polytetrafluoroethylene, cellulose acetate, polyacrylonitrile, polyamide, polyvinyl carbazole or the like on a photoconductive layer as disclosed in the Japanese Patent Publication No. 11787/1966, No. 23910/1967, No. 2965/1973, etc. (photosensitive materials of this type are utilized exclusively for complicated modified processes other than Carlson's process). The photosensitive materials of the third type include ones prepared by forming a layer for transporting conductive carriers generated within a photoconductive layer through light absorption on said photoconductive layer as disclosed in the Japanese Patent Publication No. 16198/1967, No. 5349/1970, etc. However, in the case of photosensitive materials of the first and second types, although the physical properties thereof such as the surface smoothness, adhesive property, etc. and/or flexibility admittedly improve to some extent, the electrophotographic sensitivity thereof deteriorates. Besides, in the case of the photosensitive materials of the second type, inasmuch as a more complex electrophotographic process is applied thereto, the cost of copies becomes higher. In the case of photosensitive materials of the third type, the interlayer adhesion is poor and an electric charge barrier is apt to be brought about on the interface between the photoconductive layer and the conductive carrier layer. Accordingly, when they are used repeatedly, there occur deterioration of the properties, fatigue phenomenon, residual potential, etc. and it gradually becomes impossible to form a clear-cut image.